This invention relates to a metal cable with a covering sheath of the type suitable for transmitting remote control actions by the relative axial movement between the cable and sheath which requires a very small force for its operation and may be constructed simple and at low cost.
Cables are available for transmitting remote control actions comprising substantially a metal cable which slides within a sheath the purpose of which is to form the sliding seat for the cable, to act as a reaction element and to protect the cable itself. The member of the device or machine to be controlled may be connected either to the sliding cable or to the relative sheath.
Cables of the type described comprise a sheath with a structure designed for mechanical strength, consisting substantially of a plurality of metal wires wound as a helix, the structure being lined both internally and externally. At each end of the sheath there is a terminal piece of substantially tubular form which is fixed to the sheath and provided with means for connecting it to a member. The end of said terminal piece is normally provided with a cavity in which is housed the end of a tubular element, so as to form a ball joint to enable the angular position of said element to be varied with respect to the terminal piece.
Each end of the sliding cable is provided with a cylindrical rod which can slide inside the first mentioned tubular element and is also provided with means for connecting it to a member.
Sheathed cables of the type described have certain disadvantages.
Firstly, as the cable is in contact with the inner sheath lining, the coefficient of friction between the lining and cable is not particularly small, and because of this a rather large force is generally necessary to obtain axial movements of the cable relative to the sheath.
Moreover, because of the presence of the said parts connected to each end of the sheath and cable, the manufacturing process for a sheathed cable of the type described involves numerous complicated manufacturing stages, with the result that the cable obtained by it is costly. In this respect, the terminal piece of the sheath, the tubular element connected to it and the rod fixed to the end of each cable are metal, and their construction involves mechanical operations for removing swarf and for providing permanent deformation. In addition, rather complicated assembly operations are involved in fixing them to the sheath and cable.